Fluorescent dyes are known to be particularly suitable for applications in which a highly sensitive detection reagent is desirable. Fluorescent dyes are used to impart both visible color and fluorescence to other materials. As researchers increasingly utilize fluorescent probes as research tools, the ability to select the wavelength of fluorescence becomes more important, particularly as more multiple-color applications are developed.
A variety of fluorescent dyes have been previously and extensively described, including coumarins, fluoresceins, rhodamines, rhodols, oxazines, carbocyanines, and derivatives thereof. The selection of certain substituents has been shown to be useful in adjusting the spectral properties of such dyes but there have remained regions of the visible spectrum where suitable fluorescent dyes either did not exist, or did not possess particularly favorable properties.
The dyes of the invention incorporate additional fused aromatic or heteroaromatic rings, and exhibit a shift of fluorescence emission to longer wavelength that is typically greater than 20 nm, relative to otherwise structurally similar dyes known in the art. This bathochromic spectral shift yields dyes that are particularly useful for excitation in the wavelength ranges between 400 nm and 600 nm and in particular at greater than 630 nm. Of particular importance are the dyes of the invention that exhibit absorbance maxima between 530 nm and 650 nm, as they match the principal emission lines of the mercury arc lamp (546 nm), frequency-doubled Nd-Yag laser (532 nm), Kr-ion laser (568 nm, and 647 nm) and HeNe laser (543 nm, 594 nm, and 633 nm).
Fluorescent dyes of the invention with longer wavelength absorption and emission are particularly useful in conjunction with materials of biological origin such as blood, urine, fecal matter, cells and tissues, because background or inherent fluorescence or absorption is less likely to interfere with dye detection. Furthermore, infrared dyes of the invention have enhanced utility in biological systems that are transparent at infrared wavelengths. The long wavelength dyes of the invention also have advantages in use as laser dyes, or in electronics as optical memory elements using relatively low cost illumination sources such as laser diodes.